By Dorothy Brooks
Considering the United States was declared polio-free long ago, why is there an outbreak in New York? Investigators note while there are only two countries still known to have endemic wild poliovirus or type 1 illness, most outbreaks globally are attributed to what is referred to as vaccine-derived polio, or type 2, according to public health experts who recently briefed clinicians on the outbreak in New York.1 “This is also the virus type that caused the case [of paralytic polio] in New York,” explained Farrell Tobolowsky, DO, MS, clinical task force lead for the 2022 polio response at the CDC.
Cases of the type 2 form of polio stem from the large-scale, global use of the oral polio vaccine, a solution that contains a live (but weakened) virus. “Because this vaccine contains weakened, live virus, and it is shed in the stool, it can circulate in a community,” Tobolowsky said. “If it is allowed to circulate in an underimmunized population for long enough, this strain [of the virus] can revert to a form that causes paralysis.”
Consequently, while cases of wild poliovirus have declined decade by decade, outbreaks of the disease continue today, with more than 240 cases already identified globally this year, most of which are attributed to the vaccine-derived form of the illness.2
An inactivated polio vaccine (IPV) was licensed in the U.S. in 1955 and used extensively here until the early 1960s, noted Georgina Peacock, MD, MPH, director for the immunization services division at the CDC.1,3 However, it was largely replaced by the live, attenuated oral vaccines until the late 1990s. “The nearly exclusive use of [the oral vaccine] led to the elimination of wild poliovirus from the United States in less than 20 years,” Peacock said.
However, in 1999, the CDC’s Advisory Committee on Immunization Practices recommended the exclusive use of the IPV, a step that would eliminate the shedding of live virus into the stool and any potential for vaccine-associated virus to circulate in the community, according to Peacock.1,3
Since 2000, the IPV has been the only polio vaccine used in the United States and is considered the preferred vaccine for countries not experiencing outbreaks.3 All this underscores the importance of making sure both children and adults are fully vaccinated.
REFERENCES
1. Centers for Disease Control and Prevention. Polio in New York: How to recognize and report polio, and reinforce routine childhood polio vaccination. Sept. 1, 2022.
2. Polio Global Eradication Initiative. Polio now. As of Sept. 13, 2022.
3. Centers for Disease Control and Prevention. Poliomyelitis. Page last reviewed Aug. 18, 2021.
Most outbreaks globally are attributed to vaccine-derived polio, or type 2. Cases of the type 2 form of polio stem from the large-scale, global use of the oral polio vaccine, a solution that contains a live (but weakened) virus.
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